None. The server’s identity is stored in the Windows registry.
If you cannot access the old registry “hives”, How to open a registry file from a crashed computer | @Poremsky.com
there is unfortunately no way to restore this.
That being said, if you find a file named Preferences.xml in the old database folder, you can glean the relevant data from it and insert them into your own registry.
Most important are the various ID, ...identifier strings, as well as the 4 PlexOnline... strings.
Plex server must be not running while you are doing this.
